The first U.S. troops arrive at the airport in Swidwin, Poland, on April 23, 2014. / Janek Skarzynski, AFP/Getty Images

by Tom Vanden Brook, USA TODAY

by Tom Vanden Brook, USA TODAY

WASHINGTON - The 600 paratroopers the Pentagon is dispatching to Poland and three Baltic nations to conduct live-fire training will also serve as a trip wire to Russian aggression in the region, according to military officials and analysts.

The Pentagon considers the deployment, though small, a serious marker and called on Russia to back away from Ukraine.

"Make no mistake: The Russians are the provocateurs here," said Army Col. Steve Warren, a Pentagon spokesman. "Destabilizing eastern Ukraine is a highly provocative action. Sending thousands of troops into Crimea is highly provocative. American actions are intended to reassure our allies that we are there for them."

The first 150 soldiers from the 173rd Airborne Brigade landed Wednesday in Poland. Similar units from the brigade will deploy in C-130 and C-17 cargo planes to Estonia, Latvia and Lithuania. The teams consist of riflemen, snipers and mortar men who fire 60mm shells, Warren said. All of them are expected to be in place by Monday.

"We are telling our allies that we are committed to their defense," Warren said. "And we are letting the Russians know that we're committed to the defense of our allies. That's a message that we want them to hear loud and clear."

The paratroopers, nicknamed "Sky Soldiers" from the Vicenza, Italy-based brigade, plan training missions that will culminate in live-fire exercises, including air assault by helicopter and possibly jumps from planes. Medics will train with their counterparts from Poland and the Baltic states.

"This is dangerous and complicated work," Warren said. "We take it all very seriously."

A force of 600 soldiers, of course, is no match for the 40,000 troops Russia has deployed to the Ukrainian border. There was no change to the posture of Russian forces on Wednesday, Warren said.

Russian troops, stripped of insignia that would identify them, seized Crimea, touching off the tensions in Eastern Europe and with the United States.

The crisis has spooked NATO allies in the region with echoes of the Cold War. U.S. soldiers in those countries will act as a deterrent to Russia, said Michael O'Hanlon, a military analyst at the Brookings Institution, a think tank. Long-term deterrence will require more U.S. troops in Eastern Europe, if Russia moves further into Ukraine.

"If and when Russia moves into eastern Ukraine in force, at that point, I'd want permanent stationing of U.S. forces in the Baltics and perhaps Poland, not just rotations," O'Hanlon said.

Moving large numbers of troops, and heavy equipment like armor, to the region would likely several weeks, O'Hanlon said. Most of the gear would have to be transported by sea.

Meantime, soldiers will be sleeping in World War II-style barracks or in tents in the woods as they train in Poland, Warren said.